A variety of catalysts for hydrotreating, hydrodesulfurization, and/or hydrodenitrogenation are known in the prior art and/or are commercially available. In this connection, EP 0601722 describes catalysts for hydrodesulfurization and hydrodenitrogenation of hydrocarbon oils. The catalysts therein are formed by impregnation of an alumina carrier; the impregnation solution contains at least one Group VI metal element, at least one Group VIII metal element, phosphoric acid, and an additive agent. In the impregnation solutions of EP 0601722, the additive agents include at least one dihydric or trihydric alcohol having 2 to 10 carbon atoms per molecule, and ethers of these alcohols; the amount of additive agent is such that the molar ratio of additive agent to total moles of the Group VI metal element and the Group VIII metal element is in the order of 0.05:1 to 3:1. However, during preparation of solutions according to EP 0601722, it was observed that a solution containing polyethylene glycol-200 at an additive:metal ratio of 0.22:1, a phosphorus to Group VI metal ratio of 0.60:1, and a molybdenum concentration of about 450 g/L (expressed as MoO3) contained precipitate. In contrast, for a solution in which the polyethylene glycol-200 was at an additive:metal ratio of 0.22:1, the phosphorus to Group VI metal ratio was 0.14:1, and the molybdenum concentration was about 450 g/L (expressed as MoO3), no precipitate was seen.
When forming catalysts for hydrotreating, hydrodesulfurization, and/or hydrodenitrogenation via impregnation of a support, precipitate formation in the impregnation solution is usually undesirable. Thus, the art continually strives to form impregnation solutions without precipitate from which to make catalysts with higher activities for hydrotreating, hydrodesulfurization, and/or hydrodenitrogenation.